Polyimide dry film and application thereof

Abstract

A polyimide dry film including a carrier and a polyimide layer and a method of using the same are provided. The polyimide layer contains (a) a polyimide precursor or soluble polyimide and (b) a solvent. The solvent includes a hydrophilic solvent and a hydrophobic solvent and a weight ratio of the hydrophilic solvent to the hydrophobic solvent is in the range of about 0.05 to about 2. The polyimide dry film of the present invention has water absorbability, is relatively stable even in the presence of water, and has a non-sticky surface. The resulting polyimide has excellent physical properties and can be used in a process in which water or an aqueous solution is involved to form a coverlay with excellent physical properties.

Description

BACKGROUND OF THE INVENTION1. Field of the Invention[0001]The present invention relates to a polyimide dry film, particularly a polyimide dry film applicable to a wet process, and a method of using the same.2. Description of the Related Art[0002]In recent years, it has been emphasized that electronic products should be lighter, thinner, shorter and smaller, and thus the size of various electronic parts and components has to be reduced much more. Under such a development trend, there is more room to develop a flexible printed circuit (FPC) board which has lightness, thinness, high temperature resistance and other characteristics and may be produced abundantly. The flexible printed circuit board may be found in various electronic products which are popular nowadays, such as mobile phones, liquid crystal displays, and organic light-emitting diodes. The flexible printed circuit board is produced by arranging circuits and other electronic components on a flexible substrate, which, compar...

AI Technical Summary

Benefits of technology

The polyimide dry film in this patent can be applied to a substrate without needing a high-pressure degassing machine or vacuum lamination apparatus. It can be used in a wet lamination process and has good heat resistance, dimensional stability, insulativity, and chemical resistance. The application process is simple and the apparatus is readily available, making it more cost-efficient than existing techniques.

Problems solved by technology

However, the above method requires conducting the procedures, such as processing and openings formation on a very thin coverlay, and the lamination of the coverlay to the soft board substantially relies on manual operation.

Therefore, it results in the problems, such as low yield of the process and a high cost, thus failing to satisfy requirements for high precision assembly.

In addition, a problem of adhesive overflow (adhesive bleeding) exists.

However, when the photo-imageable coverlay is laminated to a patterned circuit board by a dry lamination process, undesired gas may remain between the patterned circuit board and the photo-imageable coverlay, thus affecting reliability and quality of final products.

However, the gas bubbles are difficult to be removed completely, and may regenerate easily.

However, in most cases, the method that uses the vacuum lamination apparatus can only achieve lamination in a single-sheet manner, i.e., it is necessary to pause for a period of time after each lamination so as to remove a test piece that has been laminated and replace it with another test piece.

The method that uses the vacuum lamination apparatus is not only time-consuming and fails to satisfy an objective of rapid production, but it is also not cost-efficient due to the high cost of the apparatus.

However, the coverlay made from the epoxy resin or the acrylate resin may not be applied to high-level products due to insufficient heat resistance, insulativity, chemical resistance or mechanical strength.

Furthermore, because the photo-imageable DFSM has an organic solvent content of 1 wt % or less, it is not suitable for use in a wet lamination process.

Although the polyimide dry film has desirable heat resistance, dimensional stability, insulativity, and chemical resistance, it is not suitable for use in a wet lamination process if the solvent used is poorly compatible with water or an aqueous solution.

Moreover, polyimide and a precursor thereof (for example, polyamic acid or polyamic ester) is prone to hydrolysis, which causes chain scission or premature imidization and produces undesired low-molecular-weight polyimide precipitates, thereby affecting the quality of resulting coverlay.

Accordingly, it has been considered in the art that the polyimide dry film generally needs to be stored or processed at a low-temperature or anhydrous environment and thus is not suitable for use in a wet lamination process.

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